The majority of all inboard and outboard drives for power boats utilize a hub-type propeller. While there may be practical advantages to hub-type propulsion systems, there are many disadvantages and drawbacks especially in terms of performance and efficiency. For example, hub-type propeller units inherently experience cavitation problems. Also, most hub-type propellers are designed to be driven by an engine having a vertical drive shaft. Most vertical drive shaft internal combustion engines are of the two-cycle type and consequently tend to pollute the air and water and are not as desirable as four-cycle engines. In fact, it is difficult to adapt a four-cycle engine to a vertical drive.
Another problem associated with hub-type propeller units is that such propellers include a substantial frontal area that is non-performing and therefore creates substantial drag. Moreover, hub-type propellers are required to operate in disturbed water and consequently detracts from the performance and efficiency of hub-type propellers.